MIAMI — The Miami Beach City Commission voted Wednesday to prevent visitors from using public parking garages and lots in South Beach during two weekends in March, a major new initiative on the eve of spring break that goes further than measures the city had approved last month. Officials had previously said city-owned garages and parking lots in the entertainment district would close after 6 p.m. to everyone except Miami Beach residents and employees from March 7-10 and March 14-17, the weekends that are expected to bring the highest volume of visitors. But during a discussion Wednesday to ap…